This invention relates to a device for supplying pressurized fuel to a fuel injected engine, and more particularly to a fuel supply device for more quickly pressurizing fuel sent to the injection valves.
It has been well-known that the fuel efficiency, performance and emission control of an engine can be improved by use of a fuel injection system. With such systems, fuel must be delivered under pressure (about 30 kg/cm.sup.2) through fuel injection valves of the fuel injectors, which valves open and close as fuel is sprayed to the engine. Conventionally, the required pressure is supplied by a high pressure fuel pump driven in association with the engine's crankshaft.
However, when an engine using this conventional arrangement has been turned off for an extended period of time, internal leaks in the high pressure pump and possible leakage from open fuel injection valves cause a drop in pressure. Thus, inadequately pressurized fuel reaches the injection valves as the engine begins to turn over, leading to insufficient fuel injection and a slower starting response from the engine. This, in turn, leads to an accordingly slow build-up of pressure in the fuel distribution line, since the high pressure fuel pump is driven by the engine's crankshaft.
There is thus a circular dependence of the pressurization rate upon output from the engine, and output from the engine upon the pressure in the fuel distribution line. As a result, the length of time required to start an engine with conventional means for pressurizing the fuel ultimately depends upon the pressure in the fuel distribution line before the starting process is begun. As the engine remains off longer, the leakage of fuel increases, pressure decreases, and starting the engine will take longer.
The delay in starting the engine is compounded in some fuel supply arrangements wherein a pressure accumulation chamber is employed, which accumulates and absorbs pressure pulses caused by the pumping of the high pressure fuel pump. Including such a pressure accumulation chamber in the fuel supply device increases the volume of fuel to be pressurized. Thus, it takes even longer for the high pressure pump to pressurize the fuel distribution line to the appropriate level.
It is therefore an object of this invention to provide a fuel supply device which more quickly pressurizes the fuel distribution line, thus allowing for a shorter engine starting time than conventional arrangements provide.
The high pressure under which the fuel distribution line remains immediately after shut-down is part of the reason for fuel leakage while the engine is off. Both fuel injection valves and check valves of the high pressure pump prevent sudden decrease in pressure, but the maintained high pressure in the fuel distribution line increases the likelihood that, when the engine is shut off, fuel will leak from the supply side through the leak paths aforenoted.
It is therefore a further object of this invention to provide a method of temporarily and reversibly reducing pressure within the fuel distribution line during engine shut-down.